Electromagnetic contactor



Feb. 20, 1951 L, MERGE 2,542,835

ELECTROMAGNETIC CONTACTOR Filed Sept. 27, 1947 2 O O '17 l\t\\\\ 1 WITNESSES: INVENTOR Lawrence Pierce.

4' '1 fiwu. g 13 c. M.

ATT RNEY Patented Feb. 20, 1951 UNI TED STATES PAT OFFiCE ELECTROMAGNETIC UGNTACTOR.

Lawrence Pierce, Pittsburgh, Pa flSSignor :to WestinghouseElectric Corporation, East Pitts burgh, Pa", a corporation of Pennsylvania Application September 27, 1947, Serial N 0. 7-76;557 '2 Claims. (Cl.,200*87) My invention relates to electromagnetic relays, switches and the like contactors whose armature is biased toward one position and'magnetically moved 'to another position for controlling electric contacts by the armature movement. In a more specific aspect, my invention relates to contactors whose :contacts are normally closed by spring bias and are opened hythe energization of a magnet coil preferably energized by direct current.

It is an object of my invention to reduce. or

eliminate the tendency of a sluggish .or temporarily hesitant armature movement often encountered with such contactors. In conjunction therewith, it is also an object-of the invention to permit increasing the current carrying capacity of the contact device of such contactors, or to .re 'duce the sparking, contact burning or sticking tendency .that such contactors may show when operating with relatively high currents.

With particular reference to contactors with spring-closed and electromagnetically opened contacts, a more specific object of the invention will be explained in the following. Contacto-rs of this type usually operate poorly as current in.-

terrupting devices. In order to keep the :size of the magnet coil :as small as possible, the armature closing or biasing spring should be inst strong enough to overcome the opposing torce of the contact pressure spring. As .a result, the armature is in nearly balanced condition when the contacts are .closed. When the direct current coil is energized, the magnetic flux builds up slowly due to the inductance of thecoil. However, since the armature is nearly balanced, little flux is required to produce a magnetic :pull .sufficient to move the armature. Hence, the arm-ature movement starts :almost immediately. As long as the armature moves through its range of overt-revel, the contacts remain closed. At the moment when the moving armature starts en:- gaging the movable contact, the reaction force of the contact spring, which has been counteracting the force of the armature -closing spring, is entirely lost. Hence, the force required to continue moving the armature goes up to a much higher value. Since the magnet coil is building up its field rather slowly, it will likely not have enough pull as yet to overcome the increase in spring load that it now encounters. As a result, the armature tends to stop at the contact touch position until the coil flux has built up to a sufficient- 1y high value. Under these conditions, the contact separation occurs initially at a relatively slow rate. This results in excessive contact burning, especially if relatively high current loads are to be interrupted. Besides, the inertia of the moving armature may cause the contacts to open a little and then toreclose before they are finally separated b the increased force of the magnetic w iects (and s'accordan'ce with my invention, I design electromagnetic contactors in such a man-- nor that the coileenergized magnet or held structure and the armature of the-contactor form together not only. amain magnetic circuit or flux path .for moving the armature against its spring bias but establish :also :an auxiliary magnetic cinouit or fl path which ex ends in ma netic p rlle re atio o h ma n path nd xe t a m netic pu l on t e a m t e in he dir ti n of he rma ur prin bi s wh n he a m ture s in its biased posit n of e t- This and other features of m invention will be understood from the following description of a the embodiment exemplified by the drawin in which:

Figure .1 shows an electromagnetic contactor in side view and Fig. -2 the (same contactor .in a sectional front view, the section being taken along the plane indi'cat d m Fi 1 by th dotanddash lin enoted by Il -II.

The illustrated contactor when properly in.- stalle'd is so directed that its base plate, shown horizontally Fig. 1 is attached to a vertical wall or panel so that the arc chute of the con:- tactor lies on top and the magnet coil :at the bottom of the installed apparatus.

An insulating body 2 is firmly secured to the base plate I and :carries a standard 3 equipped with a stationary contact 4 which is conclu'ctiively connected with a tenni-na-l screw 5.. The movable contact to cooperate with "stationary contact '4 is denoted by 5. Both contacts are disposed within n arc chu e l is flanked by rc n h n such as the one denoted by 8, between which a magnetic lowou fi l is produc d bymeans of a blowout coil. 9,. This o l is el ri lly series.- connected -:b,etween the stationary contact 4 and th appe inin t rminal 5. The movable com tact 6 is mounted "on a rigid carrier H which is electrically connected by a flexible conductor I2 to a second terminal screw I3.

The field magnet of the contactor is a composite structure which has a base portion I 4, contiguous with a leg portion I5 that extends at a right angle to the base portion. A core portion I6 is firmly secured to the base portion I4 and extends in parallel to the leg portion I5- A second base portion I1 is firmly screwed to the leg portion [5 so as to form an extension of the base portion I4. A magnetizable member I8 is attached to the second base portion I1 and ex tends in parallel to leg portion I5 and core portion I6. It will be recognized that the magnetic frame or field structure just described has generally the shape of the letter E with three mutually parallel portions I5, I6, I8 extending at a right angle to the base portions I4 and IT. The control coil I9 for magnetizing the field structure is disposed on the core portion IS.

A bracket 20 is attached to the leg portion I5 and forms together therewith a pivot bearing 2I on which the armature is fulcrumed. The armature has generally the shape of a doublearmed lever, the two arms being denoted by 22 and 23. A bracket 24, attached to th arm 23 of the armature, forms abutments for two biasing or armature closing springs 25 and 25 whose respective other ends abut against adjusting screws mounted on the bracket 20. the armature arm 23 is a stirrup 26 which is equipped with a contact spring 2"! Whose lower end presses against the contact carrier II and forces it toward the armature. The contact carrier II has a pivot edge inserted into a corresponding groove 28 of the bracket structure 24 so that the carrier II with contact 6 is capable of pivotal movement about the pivot axis in groove 28 in opposition to the contact spring 21.

The member I8 has a smaller cross-section than the core member I6 and hence higher magnetic reluctance than the core portion. Member I8 is further provided with a neck portion 29 of still smaller diameter to provide a section of further increased magnetic reluctance. The top of member I8 forms a stop which abuts against the armature 23 when the latter is in the illus-- trated contact-closing position.

The above-described field structure and armature form together two magnetic circuits or fiux paths. The main magnetic circuit extends through the core portion I8, the base portion I4, the leg portion I5, and the armature arm 22. This main circuit, when magnetized by the coil I9, provides the magnetic pull for moving the armature and the associated contact structure into the contact Opening position. The second auxiliary magnetic circuit extends through the base portion I1, the member I8 and the arm 23 of the armature and extends in magnetic parallel or shunt relation to the above-mentioned main magnetic circuit. Due to the above-mentioned dimensions of the member I8 the auxiliary magnetic circuit has higher reluctance than the main circuit. When the coil I9 is energized by direct current and builds up a magnetic flux in the field and armature structure, the member I8 exerts a magnetic pull on arm 23 of the armature. This pull acts in the samedirection as the armature closing springs 25 and 25' and hence prevents the armature from starting a creeping movement before the fiux in the main magnetic circuit is strong enough to effect a rapid opening movement. When the magnetic field has built up to a value sufiicient to overcome the combined spring Attached to 4 bias and auxiliary magnetic pull, the armature movement is initiated and occurs without the above-mentioned sluggishness or hesitancy of the known devices. A definite release value is secured by the necking of member I8, at 29. The crosssection and length of portion 29 determine the flux value at which the iron becomes saturated. Hence the magnetic pull produced by the auxiliary magnetic circuit increases only to a predetermined maximum which corresponds to a definite magnitude of the increasing magnetic fiux. When this value is exceeded during the building up period of the coil energization, the magnetic pull in the main airgap between core I6 and arm 22 overpowers the holding force of the auxiliary circuit so that then the armature movement is started. Since then the pull of the main circuit is much higher than if it would be without the efiect of the auxiliary circuit and since further the biasing action of the auxiliary circuit immediately decreases once the armature movement has started, more than enough pull is available at the contact touch point to overcome the spring loading. Consequently, the hesitating tendency of the armature is eliminated. As a matter of fact after the armature starts moving, the airgap between member it and arm 23 increases to such an extent that, at the moment when the armature reaches the contact touch point, the reluctance of the auxiliary magnetic circuit is extremely large as compared with that of the main magnetic circuit so that at the point where the magnetic opening pull is supposed to be largest and where the sudden change in the spring loading must be encountered, virtually only the advantageous effect of the increased magnetization of the main circuit is effective while the opposing pull previously exerted by the auxiliary circuit has virtually completely vanished.

It will be understood by those skilled in the art on the basis of the foregoing disclosure, that contactors according to the invention can be modified in various respects, for instance, as regards the structure, design and arrangement of the magnetic and contact elements of the device without departing from the gist of the invention and within the scope of its essential features as set forth in the claims annexed hereto.

I claim as my invention:

1. A normally closed electromagnetic contactor, comprising a magnetizable field structure having a core portion and a leg portion extending substantially parallel to each other, an armature pivoted on said leg portion and having two arms of which one forms a main flux path together with said core portion and said leg portion, a stationary contact, a movable contact mounted on said other arm and capable of limited movement relative to said other arm, a spring biasing said armature toward closed position of said contacts, a contact pressure spring disposed between said movable contact and said other arm so as to be stressed in opposition to said biasing spring when said armature is in said position, a coil disposed on said core portion for moving when energized said armature toward open position or said contacts in opposition to said biasing spring, a magnetizable member disposed between said field structure and said other arm and spaced from said core portion to form an auxiliary fiux path together with said other arm for exerting magnetic pull on said other arm in the biasing direction of said biasing spring, said member extending parallel to said core portion and having over substantially its entire length a higher magnetic reluctance than said core portion, and said member having over a fraction of its length a restricted cross section so as to saturate when the attractive force of said core portion exceeds a given value sufiicient to move said armature toward said open position against the combined spring bias and magnetic pull.

2. A normally closed electromagnetic contactor, comprising a magnetizable field structure having a core portion and a leg portion extending substantially parallel to each other, an armature pivoted on said leg portion and having two arms of which one forms a main flux path together with said core portion and said leg portion, a stationary contact, a movable contact mounted on said other arm and capable of limited movement relative to said other arm, a spring biasing said armature toward closed position of said contacts, a contact pressure spring disposed between said movable contact and said other arm so as to be stressed in opposition to said biasing spring when said armature is in said position, a coil disposed on said core portion for moving when energized said armature toward open position of said contacts in opposition to said biasing spring, a magnetizable member disposed between said field structure and said other arm and spaced from said core portion to form an auxiliary flux path together with said other arm for exerting magnetic pull on said other arm in the biasing direction of said biasing spring, said member extending parallel to said core portion and having over substantially its entire length a smaller cross section than said core portion, and having a neck portion of further reduced cross section near said other arm of said armature.

LAWRENCE PIERCE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,214,355 Murphy Jan. 30, 1917 1,278,368 Montgomery Sept. 10, 1918 1,280,661 Carichoff Oct. 8, 1918 1,298,746 Lum Apr. 1, 1919 1,412,933 Gordon Apr. 18, 1922 1,525,697 Stoekle Feb. 10, 1925 1,692,604 Whittingham Nov. 20, 1928 2,231,974 Van Valkenburg Feb. 18, 1941 2,347,528 Weiser Apr. 25, 1944 2,366,984 Soheg et a1. Jan. 9, 1945 2,374,017 Iglehart et al Apr. 17, 1945 2,397,228 Young et a1 Mar. 26, 1946 2,406,216 Goldberg Aug. 20, 1946 

